Diurnal Time-Activity Budgets and Habitat Use of Ring-Necked Duck Ducklings in Northcentral Minnesota

13 Pages·1992·6.6 MB·English

by  Stephen J Maxson

Wilson Bull, 104(3), 1992, pp. 472^84
DIURNAL TIME-ACTIVITY BUDGETS AND HABITAT
USE OF RING-NECKED DUCK DUCKLINGS IN
NORTHCENTRAL MINNESOTA
Stephen J. Maxson' and Richard M. Pace, IIP
Abstract.—Westudieddiurnal time-activitybudgetsand habitatuseof36 individually
marked,classIIandIII Ring-neckedDuck(Aythacollaris)ducklingsduring 1983and 1984
in northcentral Minnesota. Overall, ducklings spent 40.9% oftheir time foraging, 30.8%
resting, 21.0% in comfort activities, 6.0% in locomotion, and 1.3% alert. Within broods,
duckling activities were synchronized. When the duckling being sampled was foraging,
resting, orengaged in comfort movements, 87%, 77%, and 56%, respectively, ofthe other
brood members were engaged in the same behavior. Although male ducklings were larger
than theirfemale siblings, we detected no sex differences in activity budgets, dive rates, or
the proportion oftime spent in subsurface vs surface feeding. Only time spent in comfort
andlocomotoractivitiesvariedbytimeofday. Timespentinallactivities,exceptcomfort,
differedbetween years. Five ofsixhensabandonedtheirbroodsbeforetheducklingscould
fly. Thereafter, ducklings spent more time foraging and less time resting and in comfort
activities. Ducklingswere neverobservedon shore.Theyspent82.6%oftheirtimeinopen
water, although use ofthis habitatcomponent was less than itsavailability(96.7%). While
in open water, ducklingsspent most oftheirtime foraging(50.9%), resting(20.6%), and in
comfort activities (19.2%). Exposed flats, consisting ofislands ofdecayed organic debris,
were used (16.0%) far in excess oftheir availability (0.3%), indicating ducklings actively
selected this habitat component where they mostly rested (65.8%) and engaged in comfort
activities(28.4%). Received 9May 1991, accepted 1 Feb. 1992.
Time-activity budget studies are useful for quantifying how ducks ap-
portion their time to cope with varying energy demands, how they cope
with various environmental changes on a daily, seasonal, and year-to-
yearbasis, and how these birds use habitat. Brood rearingisan important
phase in the annual cycle ofducks. Several time-activity budget studies
have quantified the behavior ofbrood hens and/or ducklings (e.g., Ham-
mel 1973, Siegfried et al. 1976, Joyner 1977, Ringelman and Flake 1980,
Afton 1983, Hickey and Titman 1983, Paulus 1984, Rushforth Guinn
and Batt 1985). However, none ofthese studies has sampled individually
marked ducklings ofknown sex norhaveany time-activitybudget studies
been conducted on Ring-necked Duck {Aythya collaris) broods.
The Ring-necked Duck is a small-bodied diving duck that breeds pri-
marily in the closed boreal forest of Canada. In the United States, the
' Wetland WildlifePopulationsand ResearchGroup, MinnesotaDept, ofNaturalResources, 102 23rd
St., Bemidji, Minnesota 56601.
^WildlifePopulationsand ResearchUnit, MinnesotaDept,ofNatural Resources, 500LafayetteRoad,
St.Paul,Minnesota55155.(Presentaddress:U.S.FishandWildlifeService,LouisianaCooperativeFish
and Wildlife Research Unit, Forestry, Wildlife and Fisheries Building, Louisiana State Univ., Baton
Rouge, Louisiana70803.)
472
Maxson andPace • DUCKLING ACTIVITY BUDGETS 473
largest numbers are found in the Great Lakes states (Bellrose 1976), and
it has been estimated to be the second most abundant breeding duck in
the forested areas ofMinnesota (Moyle 1964). Male Ring-necked Ducks
weigh more than females except during the ovulation and laying periods
(Hohman et al. 1988, Hier 1989). Because standard metabolic rates are
a function ofbody mass, alargerbird mustexpend more energy(and thus
require more food) to conduct any given activity than a smaller bird. If
thesexualsizedimorphismisalsopresentinducklingsitshouldcontribute
to corresponding differences in time-activity budgets, especially with re-
gard to foraging. These might be expressed as differences in total time
spent foraging, the proportion oftime spent in subsurface versus surface
foraging, or in diving rates.
MaleandfemaleRing-neckedDucksexperiencedifferentselectionpres-
sures as reflected in higher survival rates ofmales (Conroy and Eberhardt
1983). This results in adult sex ratios skewed in favor ofmales (Mendall
1958, Bellrose et al. 1961, Jahn and Hunt 1964, Anderson et al. 1969).
The sexes also have differing reproductive strategies with regard to time
and energy expenditure (Hohman 1984). Intersexual differences in sur-
vivalandreproductive strategiesmightbeevidentasearlyastheduckling
stage and could be reflected in time-activity budgets.
Divingduck hens frequentlyabandon theirbroods beforethe ducklings
can fly (Hochbaum 1944). Whether Ring-necked Duck ducklings alter
their time-activity budgets after hens depart is unknown. How Ring-
necked Duck broods modify time-activity budgets during the day or be-
tween years is also unknown. Habitat use by Ring-necked Duck broods
has not been quantified.
We documented diurnal time-activity budgets and habitat use ofRing-
necked Duck ducklings during age classes Ilb-III (i.e., ducklings 25-60
days of age) (Larson and Taber 1980) and determined whether time-
activity budgets differed by sex, time ofday, oryear and whetherthe hen
was present with the brood. We quantified the degree ofbehavioral syn-
chrony among brood members. We also documented dive rates and the
ratio ofsubsurface to surface feeding by ducklings to determine whether
these differed between sexes.
STUDY AREA AND METHODS
Broods were observed at Refuge Pond, a 45-ha wetland 7 km northeast of Bemidji,
Minnesota. This wetland was also used by broodsofMallards {Anasplatyrhynchos), Blue-
wingedTeal {A. discors). Wood Ducks{Aixsponsa), and Common Goldeneyes{Bucephala
clangula).Thewetlandisapermanentlyfloodedaquaticbedinalacustrinesystem(Cowardin
etal. 1979).A25-hafloatingmatofsedge{Carexspp.)andcattail{Typhalatifolia)covered
the northwest portion ofthe basin. The remainderofthewetland (20 ha)was largelyopen
water.
474 THE WILSON BULLETIN • Vol. 104, No. 3. September 1992
We overlaid a grid on aerial photos ofthe wetland to quantify the proportion ofeach
habitatcomponent.BecausewedidnotobserveRing-neckedDuckbroodsusingthefloating
matportionofthewetland, weincludedonlythe openportionofthebasin in ouranalysis.
Most ofthis area was classified as open water. Water depth was <1.5 m. Aquatic plants
were abundant in this zone and were dominated by large leaf pondweed (Potamogeton
amplifolius), floatingleafpondweed {P. natans), whitewaterlily{Nymphaeatuberosa), and
watershield{Braseniaschreberi). Hardstembulrush(Scirpusacutus)wasscatteredthrough-
outthe open waterzone butwastoo sparsetowarranta separateclassification. Remaining
habitatcomponentsincludedstandsofcattail, standsofhardstembulrush, smallislandsof
floatingsedge/cattail mat,andexposed flatsconsistingofislandsofdecayedorganicdebris.
Ring-neckedDuckducklingswerecapturedbynightlighting(LindmeierandJessen 1961),
sexed (Addyand MacNamara 1948), aged (Larson andTaber 1980), weighed, and banded
with a U.S. Fishand WildlifeServicealuminum legband. Wealso fittedeachwith a nasal
saddle (Sugden and Poston 1968) coded to allow individual identification. Observations
began two daysaftercapture, allowing broods to reassembleand ducklings to habituate to
nasal saddles.
Ducklings were observed with binocularsand an 80x telescope from a vehicle on a hill
overlookingthewetland. Datawerecollectedduring 1-hsamplingperiodsbetween4Aug.-
14 Sept. 1983 and 8 Aug.-13 Sept. 1984. We conducted 1-4 sample periods (x = 1.9) per
day. Ducklingactivitiesandhabitatusewererecordedbyinstantaneoussampling(Altmann
1974) at 15-sec intervals at the tone ofa metronome (Wiens et al. 1970). Activities were
classifiedas: foraging, resting, comfortmovements, locomotion,alert,andagonisticbehav-
iors(Johnsgard 1965). Foragingincluded dives, dive-pauses, and surface feeding(dabbling
and food-handling). Dive-pauses typically lasted only a few sec. Pauses lasting more than
15 sec were classified as alert or resting. Comfort movements included preening, bathing,
stretching, wing flapping, orscratching(McKinney 1965). Locomotionincludedswimming
not primarily associated with foraging, walking, and flying. During each sampling period,
oneducklingwasobservedfor30minandasecondduckling,usuallywithinthesamebrood,
was observed for the remaining 30 min. When possible, both sexes were observed during
a sampling period. We alternated which sex was observed first and varied the individuals
sampled. The day was divided into four time (CDT) blocks (1 = dawn-10:00, 2 = 10:01-
14:00, 3 = 14:01-18:00, 4 = 18:00-dusk). Within each time block, the start ofsampling
was varied from day to day so that all daylight hours were sampled overthe course ofthe
study. We also recorded whetherthe sample took place priorto (hen present) orafter(hen
absent)ahenpermanentlyabandonedherbrood.Althoughduckhenssometimesleavetheir
broodsforshortperiods(e.g.,Afton 1983,Paulus 1984),noneofoursampleswererecorded
duringtemporary absences.
During samplingperiods, we documented behavioral synchronyamong brood members
by recordingthe activityofthe focal bird at 2.5-min intervalsand then scanningtheother
brood membersandrecordingtheiractivity. Thesedatawereonlycollectedfromducklings
thatwerestill accompanied bythe brood hen, becauseafterhensdeparted, broods became
less clumped spatially, making instantaneous scansdifficult.
Thesamplingunitforactivitybudgetanalyseswasone30-minperiod.Foreachsampling
unit, the number ofinstances ofeach activity was summed and converted to percent of
time. To insure homogeneity ofvariance, thearcsin square roottransformation(Anderson
and McLean 1974)wasappliedtodatabeforeanalysis. Weestimatedcomponentsaffecting
thevarianceofeachactivityusingmaximumlikelihoodmethodswiththeBMDP3Vprogram
forgeneral mixed ANOVAs(Jennrich and Sampson 1976). Ourmodelconsistedofa fixed
component for the overall mean, another fixed component for the sex by time ofday, by
year, by hen presence category that described each datum, and three random components
Maxson andPace • DUCKLING ACTIVITY BUDGETS 475
representingthreelevelsofsampling(i.e.,broods, individualswithinabrood,andrepeated
observationson an individualduckling). Wetestedthehypothesesthatthevarianceattrib-
utable to broods and individuals was zero. These variance components did not appear to
contributesignificantly(noP < 0.25)tototalvariance. Therefore,wecollapsedouroriginal
model to one that included only a single random component (replicates within a sex by
timeofday, byyear, and by hen presencecell)andanalyzedobservedactivitieswith more
traditional MANOVAandANOVAleast squares modelsusingtheGLM procedureofthe
StatisticalAnalysisSystem(HelwigandCouncil 1979).Leastsquareestimatesofthevarious
means were determined from the appropriate models and are reported as retransformed
values.
To compare the relative amounts oftime spent in surface foraging versus subsurface
foraging(dive plus dive-pause), we subjectivelyomitted sampling units having fewerthan
15 datapointsin the foragecategorytoeliminatesamplescoveringonlya small portion of
a foraging bout (foraging bouts typically lasted 15-25 min). For the remaining sampling
units,weanalyzedtheproportionofforagingtimespentinsubsurfaceforagingusingaleast
squaresanalysisofmeansmodel(Searle 1987).Wetested 10simplecontraststhataccounted
foras much ofthe fourmain effects(sex, year, timeofday, hen presence)andall two-way
interactionsthatmissingcellmeans(6of32cells)wouldpermit. Priortoanalysisthearcsin
square root transformation was applied to thesedata.
When feasible, we also recorded the total number ofdives by the focal bird during the
30minitwassampled.Diverates(thenumberofdivesper 15-secintervalduringsubsurface
foragingbouts)werecalculatedbydividingthetotalnumberofdivesbythecombineddata
pointsinthediveanddive-pausecategories.Wechosetoomitfromanalysissamplingunits
havingfewerthan 10datapointsinthecombineddiveanddive-pausecategories. Weused
a paired/-test(SnedecorandCochran 1980)tocomparediveratesbetweensexes forthose
samplingperiods when dive rate data were obtained from both sexes.
RESULTS
Activity and habitat use data were obtained from 36 ducklings (18
male, 18 female) from six broods. We obtained 135 30-min samples from
males and 104 samples from females. Individual ducklings were sampled
from 1-33 times (median = 5).
Activitybudgets.—OvQVdAi, Ring-necked Duckducklings averaged 40.9%
oftheir time foraging, 30.8% resting, 21.0% in comfort activities, 6.0%
in locomotion, and 1.3% alert (Table 1). Agonistic activities occurred
rarely (<0.1% ofthe time) and were not analyzed statistically.
Broods often synchronized their activities (Table 2). Synchrony was
most pronounced during foraging and resting as most ofthe other brood
members foraged or rested at the same time as the focal bird. Comfort
activities were less synchronized indicating that comfort activities also
occurred when other brood members were foraging or resting.
Within broods, mean female weights at capture ranged from 77-96%
of mean male weights. No female weighed more than any of her male
siblings. However, tests for differences among activity budgets indicated
no significant effects for sex or any interacting set ofeffects that included
sex. Consequently, we omitted sex as an explanatory variable and reran
476 THE WILSON BULLETIN • Vol. 104, No. 3, September 1992
MANOVAs on the remaining three variables. The Wilk’s Lambda test
criterion indicated significant overall effects for time ofday (T’= 2.31, df
= 15, 605, P = 0.0033), year {F = 6.73, df = 5, 219, P = 0.0001), hen
presence {F= 3.99, df= 5, 219, P= 0.0018), and the interaction between
time ofday and year {F = 2.06, df = 15, 605, P = 0.0103). No overall
effects were indicated for the yearby hen presence {F= 1.84, df= 5, 219,
P = 0.1059), time ofday by hen presence {F = 0.82, df= 15, 605, P =
0.6518), or the year by time ofday by hen presence {F = 1.59, df= 15,
605, P = 0.0705) interactions. We used three-way ANOVAs to identify
which activities were influenced by these overall effects.
Onlytimespentincomfortactivities{F= 4.49, df= 3, 223,P= 0.0044)
and locomotion {F = 7.04, df= 3, 223, P = 0.0002) differed by time of
day. Comfort activities occurred most often during period 3 and least
often during period 4 (Table 1). Locomotion was highest during period
3 and lowest during period 2.
Timespentinallactivitiesexceptcomfortdifferedbetweenyears(Table
1). Ducklings spent more time foraging in 1983 than 1984 (F = 13.06,
df = 1, 223, P = 0.0004). Conversely, they spent more time resting in
1984(P= 12.78, df= 1, 223, P = 0.0004). More locomotion (P= 14.67,
df= 1, 223, P = 0.0002) and alert (F = 8.88, df= 1, 223, P = 0.0032)
were observed in 1983.
We found a significant interaction between time of day and year for
resting (P = 3.10, df= 3, 223, P = 0.0278), locomotion (P = 5.03, df=
3, 223,P= 0.0021), andalert(P= 3.18, df= 3, 223,P= 0.0250). Whereas
resting occurred least often in time periods 2 and 4 in 1983, resting
occurred most often during these periods in 1984 (Table 1). In 1983,
locomotion showed an increasing trend from time periods 1 to 3. How-
ever, in 1984 there was a sharp decline in locomotion between time
periods 1 and 2. Alert showed an increasing trend throughout the day in
1983 but in 1984 showed decreases in time period 2 and especially pe-
riod 4.
All six brood hens abandoned their ducklings during the study period.
One left two days after herducklings achieved flight capability. The other
hens departed 3, 4, 8, 10, and 19 days before their ducklings could fly.
These departures did not appear related to the disturbance caused by
nightlighting operations as hens departed an average of 12.2 days after
their ducklings were captured. Typically, ducklings remained together as
a brood for the first few days after being abandoned. Gradually, they
became more independent and spread out more widely on the pond.
Ducklingsbegan makingshort flightswhen two months oldanddispersed
from the pond 2-5 days later.
Afterhensabandoned theirbroods, ducklings spent moretime foraging
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478 THE WILSON BULLETIN • Vol. 104, No. 3, September 1992
Table 2
ComparisonofActivities Between Sample BirdsandOther Brood Members
Activity(%)ofotherbroodmembers
samplebird Samplebird members Foraging Comfort Rest Locomotion
Foraging 100 643 87.3 6.8 5.1 0.8
Resting 100 638 3.3 17.1 77.7 1.9
Comfort 58 366 22.9 56.0 18.6 2.5
’Numberofdatapointsobtainedat2.5-minintervalsduringsamples.
{F= 14.31, df= 1, 223, P= 0.0002) and less time in comfort {F= 10.26,
df= 1, 223, P = 0.0016) and resting {F = 7.49, df= 1, 223, P = 0.0067)
than they did while the hen was present (Table 3). Time spent in loco-
motion and alert remained unchanged.
We had 104 30-min samples for contrast analyses ofsubsurface versus
surface foraging. No sex or time ofday differences were found. The only
explanatory variables making significant contributions toward overall
variance in the proportion offoraging time spent in subsurface foraging
were year {F = 25.49, df= 1, 78, P = 0.0001) and year by hen presence
interactions {F = 8.46, df = 1, 78, P = 0.0047). Therefore, we ran an
ANOVAmodeltoproduceestimatesofmeansfortheyearbyhenpresence
interaction. These indicated that the effect of the brood hen’s presence
was greater in 1984 than in 1983. After brood hens departed in 1983,
ducklings spent a somewhat greater proportion oftheir foraging time in
subsurface foraging(77.1%—present vs 95.8%—absent). However, in 1984
theproportionofsubsurfaceforagingdecreasedmarkedlyafterbroodhens
departed (93.6%—present vs 49.1%—absent).
Table 3
Mean PercentageofTime DucklingsSpent in Each Activitywhenthe Brood Hen
Was Presentor Absent^
Activity Henpresent Henabsent
Foraging 32.2 49.6
Comfort 23.6 18.3
Rest 37.2 24.4
Locomotion 6.0 6.0
Alert 1.0 1.7
Nb 98 141
•Original analyses were conducted using arcsine-transformed proportions. Depicted values are retransformed least
squaresmeansfromtheappropriatemodel.
”Numberof30-minsamples.
Maxson andPace • DUCKLING ACTIVITY BUDGETS 479
Table 4
Ring-necked Duck Duckling Habitat Use Vs Availabilityand Duckling
Time-activity Budgetswithin Each HabitatComponenton Refuge Pond
Activitywithinhabitats(%)
Avail-
ability Use For- Loco-
Habitatcomponent {%) (%) N“ aging Comfort Rest motion Alert
Open water 96.7 82.6 23,562 50.9 19.2 20.6 7.7 1.6
Exposed flat 0.3 16.0 4570 3.5 28.4 65.8 1.1 1.3
Bulrush stand 0.9 1.1 313 92.0 5.8 0.6 0.6 1.0
Floatingmat island 0.7 0.3 82 0.0 50.0 48.8 0.2 0.0
Cattail stand 1.4 0.0 0 0.0 0.0 0.0 0.0 0.0
’Numberofinstancesfocalducklingswererecordedineachhabitatcomponent.
We recorded 5043 foraging dives during 98 30-min sampling units.
The overall mean dive rate was 0.874 ± 0.181(SD) dives per 15-sec
interval. For 15 sampling periods in which data were obtained from both
sexes, dive rates did not differ by sex {t = 2.01, df= 14, P = 0.0637).
Habitat Mineral soil made up 77% ofthe shoreline ofthe pond
whilefloatingsedge/cattailmatcomprisedtheremainder. However, duck-
lings were never observed on shore norwere theyever observed in cattail
standsalongthepondedge. Bulrushstandsandsmallfloatingsedge/cattail
mat islands appeared to be used in proportion to their availability (Table
4). Ducklingsspentthegreatmajorityoftheirtimeinopenwater,although
use of this habitat component was somewhat less than its availability.
Exposed flats were used far in excess oftheir availability, indicating that
broods actively sought out this habitat component.
Ducklings used open water primarily for foraging, but substantial
amounts of comfort and resting occurred there as well (Table 4). The
small amountoftime spentin bulrush standswasalmostexclusively used
for foraging. On the other hand, exposed flats and floating sedge/cattail
mat islands were used primarily for resting and comfort activities.
DISCUSSION
Because ofthe sexual size dimorphism and differing intersex survival
and reproductive strategies exhibited by adult Ring-necked Ducks, it can
bearguedthatsexdifferencesshouldbeevidentfromthetimeofhatching.
This appears to be the case with regard to size dimorphism but not in
other aspects. Compared to other stages in their life cycle, ducklings of
both sexes experience relatively similar energy demands associated with
growth and development. At this stage, intersex energy budget compar-
isons are not complicated by differential costs ofcourtship, gamete pro-
480 THE WILSON BULLETIN • Vol. 104, No. 3, September 1992
duction, molt, etc. Major activities among brood members were syn-
chronized, and both sexes foraged together in the same habitats, further
indicatingthat intersex survival strategies are not markedly different dur-
ing this period. Nevertheless, based on the size difference alone, we ex-
pected to find sex differences in time-activity budgets particularly asso-
ciated with foraging. However, we detected no significant differences in
activity budgets based on sex, nor did we find sex differences in the
proportion offoraging time spent in subsurface versus surface feeding or
in diving rates. Several factors may have accounted for this. The range
of duckling age (and thus different mass) over which we sampled may
have obscured subtle sex differences in foraging time or technique. Ad-
ditionally, our most direct comparison (dive rates) had a small sample
size and thus low power. Further, males may have selected a slightly
different diet than females or there could have been sex differences in
nocturnal activity. We were unable to measure either ofthese factors.
Most time-activity budget studies ofducklings have noted behavioral
changes during the day, especially with regard to foraging. Early morning
and late afternoon peaks in foraging have been reported for Blue-winged
Teal, Mallard, and Ruddy Duck {Oxyurajamaicensis) ducklings (Joyner
1977, Ringelman and Flake 1980). Mottled Duck {Anasfulvigula) duck-
lingsforagedmostinthemorningandlessduringmiddaybeforeincreasing
foraging at night (Paulus 1984). Mendall (1958), though lacking quanti-
tative data, reported that Ring-necked Duck broods tended to be more
active in morning and evening but that feeding and resting periods oc-
curred frequentlythroughoutthedaywith littleevidenceoffixedroutines.
Incontrast, wedidnotdetectdifferencesintimespentforagingthroughout
the daylight hours. Furthermore, time of day differences in resting, lo-
comotion, and alert were inconsistent between years. The extent Ring-
necked Duck duckling time-activity budgets change at night is unknown.
During nightlighting operations, Minnesota Dept, ofNatural Resources
duck banding crews frequently observe broods of Ring-necked Ducks
foraging (R. T. Eberhardt, pers. comm.).
Differences between years for all activities except comfort were likely
related to changes in food abundance or availability on the pond. During
age classes II and III, Ring-necked Duck ducklings eat a variety ofplants
andanimals(Mendall 1958, Hohman 1985, McAuleyandLongcore 1988).
Althoughjuvenile Ring-necked Ducksexhibitpreferencesforcertainfoods,
availability plays a prominent role in food selection (Hohman 1985).
Hohman (1984, 1985) noted year-to-year changes in foods available to
Ring-necked Ducks and found that contributions ofindividual food spe-
cies in class II Ring-necked Duck duckling diets differed between years
Maxson andPace • DUCKLING ACTIVITY BUDGETS 481
in northwestern Minnesota. Ifone assumes that nutritional needs ofclass
II and III ducklings remain the same from yearto yearand that ducklings
attempt to forage efficiently, then the amount of time spent foraging at
any particular stage of their development should be a function of food
abundance or availability. As sufficient food becomes easier to obtain,
less foraging time is required. Relationships between food levels and the
amountoftime spent foraginghavebeen notedin otherwaterfowl (Paulus
1988) as well as in non-waterfowl species (e.g., Maxson and Oring 1980).
The onlynotableenvironmental differencebetweenyearswasthatAugust
pond levels were 16.5 cm lower in 1984. This was the lowest August
water level recorded on the pond during the 1979-1984 period (R. T.
Eberhardt, unpubl. data) and it may have influenced abundance or avail-
ability ofduckling foods. Further evidence ofchanges in foods was the
fact that duckling foraging tactics differed between years. In 1984, par-
ticularly during the period after brood hens departed, ducklings spent
considerably more time surface feeding (primarily dabbling) than during
other phases ofour study.
Given that time is limited, any change in time spent in one activity
must be reflected in a corresponding change in time spent in other activ-
We
ities. believe that the driving factors determining duckling time-ac-
tivity budgets were requirements for foraging and feather maintenance,
and that, in general, other activities (especially resting) filled in any time
gaps remaining after these needs had been met. Time spent in comfort
activities did not differbetween years, likely because a certain proportion
of time is required for feather maintenance regardless of other factors.
When foraging time decreased in 1984, this time gap was compensated
for primarily by increased time spent resting. An inverse relationship
between time spent foraging and resting has also been noted in other
waterfowl (Paulus 1988). Thegreateramount oftime spentin locomotion
in 1983 was associated with the higher foraging and alert time that year.
Locomotion was recorded primarily as broods travelled between foraging
sites, between foraging and loafing sites, or as they moved away from
potential predators.
Afterhens abandoned theirbroods, ducklings spent more time foraging
while spending less time resting and in comfort activities. Several expla-
nations are possible. As ducklings approach adult size they require in-
creased amounts offood based on the increase in their body mass alone.
Without the hen to help guide them to good feeding locations, ducklings
may initially be less efficient in finding sufficient food, although this may
entail only a minor behavioral adjustment as ducklings had already been
foraging on the pond 40-60 days. Also, there may have been some late